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SDL_8SVX

SDL_8SVX is a package containing a library for playing 8SVX instruments as well as command-line player: 8svxplayer.

Prerequisites

In order to build and use this package the following libraries are required:

• libiff, in order to parse IFF files
• lib8svx, in order to understand 8SVX application chunks, fibonacci delta compression/decompression and to conveniently access 8SVX instrument properties
• SDL, is used as a portability layer to handle input and graphics
• SDL_mixer, is used for mixing audio chunks
• libresample, is used to resample the samples to acceptable frequencies. I have downloaded the Debian version and the corresponding Debian patches providing a CMake build interface

Installation

Compilation and installation of this library is straight forward, by using the standard GNU autotools build instructions:

$ ./configure
$ make
$ make install

More details about the installation process can be found in the INSTALL file included in this package.

Using the SDL_8SVX API

The SDL_8SVX package provides an API that can be used to read IFF files containing 8SVX instruments and allows easy usage of these instruments in SDL applications.

Full API documentation can be found in the doc/apidox directory of this package.

Generating an instruments set

An 8SVX file typically provides one single FORM representing an instrument, but could also encapsulate multiple instruments and other types of forms, in so called "IFF scrap files". The SDL_8SVX_Set struct provides an interface to access all 8SVX instruments in a particular IFF file:

#include <set.h>

SDL_8SVX_Set *set = SDL_8SVX_createSetFromFilename("somefile.IFF");

if(set != NULL && set->instrumentsLength > 0)
{
    /* Open an instrument */

    return 0;
}
else
    return 1; /* Cannot find any instruments to render samples from */

The above code fragment generates an instruments set directly from a file with a given filename. In addition to generating sets from file names, it is also possible to generate a set from a file descriptor (through: SDL_8SVX_createSetFromFd()) or an IFF_Chunk (through: SDL_8SVX_createSetFromIFFChunk()).

When the work is done, a set must be deallocated from heap memory, through:

SDL_8SVX_freeSet(set);

Composing an instrument for audio playback

Using the set API, we can retrieve an instrument from the IFF file to render samples from to the audio buffer:

#include <set.h>

SDL_8SVX_Instrument *instrument = SDL_8SVX_createInstrumentFromSet(set, 0, AUDIO_S16SYS, 22050);

The above function invocation generates an SDL_8SVX_Instrument struct from the first entry in the IFF file, in signed 16-bit format (with the same endianness as the host system) using a sample rate frequency of 22050.

We can obtain the corresponding audio sample chunks from the generated SDL_8SVX_Instrument struct and pass them to an audio channel:

#include <stdio.h>
#include <SDL_mixer.h>
#include <instrument.h>

unsigned int i;

/* Iterate over all sample audio chunks provided by the instrument */
for(i = 0; i < instrument->mixChunksLength; i++)
{
    int channel;

    /* Fetch a sample */
    Mix_Chunk *mixChunk = &instrument->mixChunks[i];

    /* Play the sample on channel 0 */
    if((channel = Mix_PlayChannel(-1, mixChunk, 0)) == -1)
    {
        fprintf(stderr, "Cannot play sample!\n");
        return 1;
    }

    /* Wait for the channel to finish playing */
    while(Mix_Playing(channel) != 0)
        ;
}

Consult the SDL_mixer API documentation for more details on how to set up the required audio infrastructure.

When the work is done, we must deallocate the instrument with the following instruction:

#include <instrument.h>

SDL_8SVX_freeInstrument(instrument);

8SVX player command-line utility

This package also includes a command-line utility: 8svxplayer that exposes most of the API's features as command-line options. For more information, run:

$ 8svxplayer --help

License

This library is available under the zlib license